Method for triggering a burffer status reporting and a device therefor

ABSTRACT

The present invention relates to a wireless communication system. More specifically, the present invention relates to a method and a device for triggering a buffer status reporting in the wireless communication system, the method comprising: calculating an amount of first DAT when the first data is arrived in a protocol entity, wherein the amount of first DAT is less than a threshold; calculating an amount of second DAT when the second data is arrived in the protocol entity, wherein the second data is arrived after the first data is arrived in the protocol entity; and triggering a buffer status report if the amount of second DAT is more than the threshold.

TECHNICAL FIELD

The present invention relates to a wireless communication system and,more particularly, to a method for triggering a buffer status reportingand a device therefor.

BACKGROUND ART

As an example of a mobile communication system to which the presentinvention is applicable, a 3rd Generation Partnership Project Long TermEvolution (hereinafter, referred to as LTE) communication system isdescribed in brief.

FIG. 1 is a view schematically illustrating a network structure of anE-UMTS as an exemplary radio communication system. An Evolved UniversalMobile Telecommunications System (E-UMTS) is an advanced version of aconventional Universal Mobile Telecommunications System (UMTS) and basicstandardization thereof is currently underway in the 3GPP. E-UMTS may begenerally referred to as a Long Term Evolution (LTE) system. For detailsof the technical specifications of the UMTS and E-UMTS, reference can bemade to Release 7 and Release 8 of “3rd Generation Partnership Project;Technical Specification Group Radio Access Network”.

Referring to FIG. 1, the E-UMTS includes a User Equipment (UE), eNode Bs(eNBs), and an Access Gateway (AG) which is located at an end of thenetwork (E-UTRAN) and connected to an external network. The eNBs maysimultaneously transmit multiple data streams for a broadcast service, amulticast service, and/or a unicast service.

One or more cells may exist per eNB. The cell is set to operate in oneof bandwidths such as 1.25, 2.5, 5, 10, 15, and 20 MHz and provides adownlink (DL) or uplink (UL) transmission service to a plurality of UEsin the bandwidth. Different cells may be set to provide differentbandwidths. The eNB controls data transmission or reception to and froma plurality of UEs. The eNB transmits DL scheduling information of DLdata to a corresponding UE so as to inform the UE of a time/frequencydomain in which the DL data is supposed to be transmitted, coding, adata size, and hybrid automatic repeat and request (HARM)-relatedinformation. In addition, the eNB transmits UL scheduling information ofUL data to a corresponding UE so as to inform the UE of a time/frequencydomain which may be used by the UE, coding, a data size, andHARQ-related information. An interface for transmitting user traffic orcontrol traffic may be used between eNBs. A core network (CN) mayinclude the AG and a network node or the like for user registration ofUEs. The AG manages the mobility of a UE on a tracking area (TA) basis.One TA includes a plurality of cells.

Although wireless communication technology has been developed to LTEbased on wideband code division multiple access (WCDMA), the demands andexpectations of users and service providers are on the rise. Inaddition, considering other radio access technologies under development,new technological evolution is required to secure high competitivenessin the future. Decrease in cost per bit, increase in serviceavailability, flexible use of frequency bands, a simplified structure,an open interface, appropriate power consumption of UEs, and the likeare required.

DISCLOSURE Technical Problem

An object of the present invention devised to solve the problem lies ina method and device for a method for triggering a buffer statusreporting. The technical problems solved by the present invention arenot limited to the above technical problems and those skilled in the artmay understand other technical problems from the following description.

Technical Solution

The object of the present invention can be achieved by providing amethod for operating by an apparatus in wireless communication system,the method comprising; calculating an amount of first DAT when the firstdata is arrived in a protocol entity, wherein the amount of first DAT isless than a threshold; calculating an amount of second DAT when thesecond data is arrived in the protocol entity, wherein the second datais arrived after the first data is arrived in the protocol entity; andtriggering a buffer status report if the amount of second DAT is morethan the threshold.

In another aspect of the present invention provided herein is anapparatus in the wireless communication system, the apparatuscomprising: an RF (radio frequency) module; and a processor configuredto control the RF module, wherein the processor is configured tocalculate an amount of first DAT when the first data is arrived in aprotocol entity, wherein the amount of first DAT is less than athreshold, to calculate an amount of second DAT when the second data isarrived in the protocol entity, wherein the second data is arrived afterthe first data is arrived in the protocol entity, and to trigger abuffer status report if the amount of second DAT is more than thethreshold.

Preferably, the method further comprises: setting an amount of DAT for afirst logical channel as the calculated amount of first DAT and anamount of DAT for a second logical channel as ‘zero’, if the amount offirst DAT is less than the threshold, wherein the first logical channelis for the first BS and the second logical channel is for the second BS.

Preferably, the method further comprises: dividing the calculated amountof second DAT into the amount of DAT for the first logical channel andthe amount of DAT for the second logical channel based on ratio if theamount of second DAT is equal to or more than the threshold.

Preferably, wherein the buffer status report is transmitted to thesecond BS.

Preferably, the method further comprises: receiving the threshold fromat least the first BS or the second BS.

Preferably, wherein the protocol entity is a Packet Data ConvergenceProtocol (PDCP) entity.

Preferably, wherein PDCP entity has two Radio Link Control (RLC)entities and two Medium Access Control (MAC) entities for one logicalchannel.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

Advantageous Effects

According to the present invention, triggering a buffer status reportingcan be efficiently performed in a wireless communication system.Specifically, the UE can calculate each amount of data available fortransmission to each base station and trigger the buffer statusreporting in dual connectivity system.

It will be appreciated by persons skilled in the art that that theeffects achieved by the present invention are not limited to what hasbeen particularly described hereinabove and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention.

FIG. 1 is a diagram showing a network structure of an Evolved UniversalMobile Telecommunications System (E-UMTS) as an example of a wirelesscommunication system;

FIG. 2A is a block diagram illustrating network structure of an evolveduniversal mobile telecommunication system (E-UMTS), and FIG. 2B is ablock diagram depicting architecture of a typical E-UTRAN and a typicalEPC;

FIG. 3 is a diagram showing a control plane and a user plane of a radiointerface protocol between a UE and an E-UTRAN based on a 3rd generationpartnership project (3GPP) radio access network standard;

FIG. 4 is a diagram of an example physical channel structure used in anE-UMTS system;

FIG. 5 is a diagram for carrier aggregation;

FIG. 6 is a conceptual diagram for dual connectivity between a MasterCell Group (MCG) and a Secondary Cell Group (SCG);

FIG. 7a is a conceptual diagram for C-Plane connectivity of basestations involved in dual connectivity, and FIG. 7b is a conceptualdiagram for U-Plane connectivity of base stations involved in dualconnectivity;

FIG. 8 is a conceptual diagram for radio protocol architecture for dualconnectivity;

FIG. 9 is a diagram for a general overview of the LTE protocolarchitecture for the downlink;

FIG. 10 is a diagram for prioritization of two logical channels forthree different uplink grants;

FIG. 11 is a diagram for signaling of buffer status and power-headroomreports;

FIG. 12 is a conceptual diagram for one of radio protocol architecturefor dual connectivity;

FIG. 13 is a conceptual diagram for reporting amount of data availablefor transmission according to embodiments of the present invention;

FIG. 14 is a conceptual diagram for triggering a buffer status reportingaccording to embodiments of the present invention;

FIG. 15 is conceptual diagram an exemplary according to embodiments ofthe present invention; and

FIG. 16 is a block diagram of a communication apparatus according to anembodiment of the present invention.

BEST MODE

Universal mobile telecommunications system (UMTS) is a 3rd Generation(3G) asynchronous mobile communication system operating in wideband codedivision multiple access (WCDMA) based on European systems, globalsystem for mobile communications (GSM) and general packet radio services(GPRS). The long-term evolution (LTE) of UMTS is under discussion by the3rd generation partnership project (3GPP) that standardized UMTS.

The 3GPP LTE is a technology for enabling high-speed packetcommunications. Many schemes have been proposed for the LTE objectiveincluding those that aim to reduce user and provider costs, improveservice quality, and expand and improve coverage and system capacity.The 3G LTE requires reduced cost per bit, increased serviceavailability, flexible use of a frequency band, a simple structure, anopen interface, and adequate power consumption of a terminal as anupper-level requirement.

Hereinafter, structures, operations, and other features of the presentinvention will be readily understood from the embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings. Embodiments described later are examples in which technicalfeatures of the present invention are applied to a 3GPP system.

Although the embodiments of the present invention are described using along term evolution (LTE) system and a LTE-advanced (LTE-A) system inthe present specification, they are purely exemplary. Therefore, theembodiments of the present invention are applicable to any othercommunication system corresponding to the above definition. In addition,although the embodiments of the present invention are described based ona frequency division duplex (FDD) scheme in the present specification,the embodiments of the present invention may be easily modified andapplied to a half-duplex FDD (H-FDD) scheme or a time division duplex(TDD) scheme.

FIG. 2A is a block diagram illustrating network structure of an evolveduniversal mobile telecommunication system (E-UMTS). The E-UMTS may bealso referred to as an LTE system. The communication network is widelydeployed to provide a variety of communication services such as voice(VoIP) through IMS and packet data.

As illustrated in FIG. 2A, the E-UMTS network includes an evolved UMTSterrestrial radio access network (E-UTRAN), an Evolved Packet Core (EPC)and one or more user equipment. The E-UTRAN may include one or moreevolved NodeB (eNodeB) 20, and a plurality of user equipment (UE) 10 maybe located in one cell. One or more E-UTRAN mobility management entity(MME)/system architecture evolution (SAE) gateways 30 may be positionedat the end of the network and connected to an external network.

As used herein, “downlink” refers to communication from eNodeB 20 to UE10, and “uplink” refers to communication from the UE to an eNodeB. UE 10refers to communication equipment carried by a user and may be alsoreferred to as a mobile station (MS), a user terminal (UT), a subscriberstation (SS) or a wireless device.

FIG. 2B is a block diagram depicting architecture of a typical E-UTRANand a typical EPC.

As illustrated in FIG. 2B, an eNodeB 20 provides end points of a userplane and a control plane to the UE 10. MME/SAE gateway 30 provides anend point of a session and mobility management function for UE 10. TheeNodeB and MME/SAE gateway may be connected via an S1 interface.

The eNodeB 20 is generally a fixed station that communicates with a UE10, and may also be referred to as a base station (BS) or an accesspoint. One eNodeB 20 may be deployed per cell. An interface fortransmitting user traffic or control traffic may be used between eNodeBs20.

The MME provides various functions including NAS signaling to eNodeBs20, NAS signaling security, AS Security control, Inter CN node signalingfor mobility between 3GPP access networks, Idle mode UE Reachability(including control and execution of paging retransmission), TrackingArea list management (for UE in idle and active mode), PDN GW andServing GW selection, MME selection for handovers with MME change, SGSNselection for handovers to 2G or 3G 3GPP access networks, Roaming,Authentication, Bearer management functions including dedicated bearerestablishment, Support for PWS (which includes ETWS and CMAS) messagetransmission. The SAE gateway host provides assorted functions includingPer-user based packet filtering (by e.g. deep packet inspection), LawfulInterception, UE IP address allocation, Transport level packet markingin the downlink, UL and DL service level charging, gating and rateenforcement, DL rate enforcement based on APN-AMBR. For clarity MME/SAEgateway 30 will be referred to herein simply as a “gateway,” but it isunderstood that this entity includes both an MME and an SAE gateway.

A plurality of nodes may be connected between eNodeB 20 and gateway 30via the S1 interface. The eNodeBs 20 may be connected to each other viaan X2 interface and neighboring eNodeBs may have a meshed networkstructure that has the X2 interface.

As illustrated, eNodeB 20 may perform functions of selection for gateway30, routing toward the gateway during a Radio Resource Control (RRC)activation, scheduling and transmitting of paging messages, schedulingand transmitting of Broadcast Channel (BCCH) information, dynamicallocation of resources to UEs 10 in both uplink and downlink,configuration and provisioning of eNodeB measurements, radio bearercontrol, radio admission control (RAC), and connection mobility controlin LTE_ACTIVE state. In the EPC, and as noted above, gateway 30 mayperform functions of paging origination, LTE-IDLE state management,ciphering of the user plane, System Architecture Evolution (SAE) bearercontrol, and ciphering and integrity protection of Non-Access Stratum(NAS) signaling.

The EPC includes a mobility management entity (MME), a serving-gateway(S-GW), and a packet data network-gateway (PDN-GW). The MME hasinformation about connections and capabilities of UEs, mainly for use inmanaging the mobility of the UEs. The S-GW is a gateway having theE-UTRAN as an end point, and the PDN-GW is a gateway having a packetdata network (PDN) as an end point.

FIG. 3 is a diagram showing a control plane and a user plane of a radiointerface protocol between a UE and an E-UTRAN based on a 3GPP radioaccess network standard. The control plane refers to a path used fortransmitting control messages used for managing a call between the UEand the E-UTRAN. The user plane refers to a path used for transmittingdata generated in an application layer, e.g., voice data or Internetpacket data.

A physical (PHY) layer of a first layer provides an information transferservice to a higher layer using a physical channel. The PHY layer isconnected to a medium access control (MAC) layer located on the higherlayer via a transport channel. Data is transported between the MAC layerand the PHY layer via the transport channel. Data is transported betweena physical layer of a transmitting side and a physical layer of areceiving side via physical channels. The physical channels use time andfrequency as radio resources. In detail, the physical channel ismodulated using an orthogonal frequency division multiple access (OFDMA)scheme in downlink and is modulated using a single carrier frequencydivision multiple access (SC-FDMA) scheme in uplink.

The MAC layer of a second layer provides a service to a radio linkcontrol (RLC) layer of a higher layer via a logical channel. The RLClayer of the second layer supports reliable data transmission. Afunction of the RLC layer may be implemented by a functional block ofthe MAC layer. A packet data convergence protocol (PDCP) layer of thesecond layer performs a header compression function to reduceunnecessary control information for efficient transmission of anInternet protocol (IP) packet such as an IP version 4 (IPv4) packet oran IP version 6 (IPv6) packet in a radio interface having a relativelysmall bandwidth.

A radio resource control (RRC) layer located at the bottom of a thirdlayer is defined only in the control plane. The RRC layer controlslogical channels, transport channels, and physical channels in relationto configuration, re-configuration, and release of radio bearers (RBs).An RB refers to a service that the second layer provides for datatransmission between the UE and the E-UTRAN. To this end, the RRC layerof the UE and the RRC layer of the E-UTRAN exchange RRC messages witheach other.

One cell of the eNB is set to operate in one of bandwidths such as 1.25,2.5, 5, 10, 15, and 20 MHz and provides a downlink or uplinktransmission service to a plurality of UEs in the bandwidth. Differentcells may be set to provide different bandwidths.

Downlink transport channels for transmission of data from the E-UTRAN tothe UE include a broadcast channel (BCH) for transmission of systeminformation, a paging channel (PCH) for transmission of paging messages,and a downlink shared channel (SCH) for transmission of user traffic orcontrol messages. Traffic or control messages of a downlink multicast orbroadcast service may be transmitted through the downlink SCH and mayalso be transmitted through a separate downlink multicast channel (MCH).

Uplink transport channels for transmission of data from the UE to theE-UTRAN include a random access channel (RACH) for transmission ofinitial control messages and an uplink SCH for transmission of usertraffic or control messages. Logical channels that are defined above thetransport channels and mapped to the transport channels include abroadcast control channel (BCCH), a paging control channel (PCCH), acommon control channel (CCCH), a multicast control channel (MCCH), and amulticast traffic channel (MTCH).

FIG. 4 is a view showing an example of a physical channel structure usedin an E-UMTS system. A physical channel includes several subframes on atime axis and several subcarriers on a frequency axis. Here, onesubframe includes a plurality of symbols on the time axis. One subframeincludes a plurality of resource blocks and one resource block includesa plurality of symbols and a plurality of subcarriers. In addition, eachsubframe may use certain subcarriers of certain symbols (e.g., a firstsymbol) of a subframe for a physical downlink control channel (PDCCH),that is, an L1/L2 control channel. In FIG. 4, an L1/L2 controlinformation transmission area (PDCCH) and a data area (PDSCH) are shown.In one embodiment, a radio frame of 10 ms is used and one radio frameincludes 10 subframes. In addition, one subframe includes twoconsecutive slots. The length of one slot may be 0.5 ms. In addition,one subframe includes a plurality of OFDM symbols and a portion (e.g., afirst symbol) of the plurality of OFDM symbols may be used fortransmitting the L1/L2 control information. A transmission time interval(TTI) which is a unit time for transmitting data is 1 ms.

A base station and a UE mostly transmit/receive data via a PDSCH, whichis a physical channel, using a DL-SCH which is a transmission channel,except a certain control signal or certain service data. Informationindicating to which UE (one or a plurality of UEs) PDSCH data istransmitted and how the UE receive and decode PDSCH data is transmittedin a state of being included in the PDCCH.

For example, in one embodiment, a certain PDCCH is CRC-masked with aradio network temporary identity (RNTI) “A” and information about datais transmitted using a radio resource “B” (e.g., a frequency location)and transmission format information “C” (e.g., a transmission blocksize, modulation, coding information or the like) via a certainsubframe. Then, one or more UEs located in a cell monitor the PDCCHusing its RNTI information. And, a specific UE with RNTI “A” reads thePDCCH and then receive the PDSCH indicated by B and C in the PDCCHinformation.

FIG. 5 is a diagram for carrier aggregation.

Carrier aggregation technology for supporting multiple carriers isdescribed with reference to FIG. 5 as follows. As mentioned in theforegoing description, it may be able to support system bandwidth up tomaximum 100 MHz in a manner of bundling maximum 5 carriers (componentcarriers: CCs) of bandwidth unit (e.g., 20 MHz) defined in a legacywireless communication system (e.g., LTE system) by carrier aggregation.Component carriers used for carrier aggregation may be equal to ordifferent from each other in bandwidth size. And, each of the componentcarriers may have a different frequency band (or center frequency). Thecomponent carriers may exist on contiguous frequency bands. Yet,component carriers existing on non-contiguous frequency bands may beused for carrier aggregation as well. In the carrier aggregationtechnology, bandwidth sizes of uplink and downlink may be allocatedsymmetrically or asymmetrically.

Multiple carriers (component carriers) used for carrier aggregation maybe categorized into primary component carrier (PCC) and secondarycomponent carrier (SCC). The PCC may be called P-cell (primary cell) andthe SCC may be called S-cell (secondary cell). The primary componentcarrier is the carrier used by a base station to exchange traffic andcontrol signaling with a user equipment. In this case, the controlsignaling may include addition of component carrier, setting for primarycomponent carrier, uplink (UL) grant, downlink (DL) assignment and thelike. Although a base station may be able to use a plurality ofcomponent carriers, a user equipment belonging to the corresponding basestation may be set to have one primary component carrier only. If a userequipment operates in a single carrier mode, the primary componentcarrier is used. Hence, in order to be independently used, the primarycomponent carrier should be set to meet all requirements for the dataand control signaling exchange between a base station and a userequipment.

Meanwhile, the secondary component carrier may include an additionalcomponent carrier that can be activated or deactivated in accordancewith a required size of transceived data. The secondary componentcarrier may be set to be used only in accordance with a specific commandand rule received from a base station. In order to support an additionalbandwidth, the secondary component carrier may be set to be usedtogether with the primary component carrier. Through an activatedcomponent carrier, such a control signal as a UL grant, a DL assignmentand the like can be received by a user equipment from a base station.Through an activated component carrier, such a control signal in UL as achannel quality indicator (CQI), a precoding matrix index (PMI), a rankindicator (RI), a sounding reference signal (SRS) and the like can betransmitted to a base station from a user equipment.

Resource allocation to a user equipment can have a range of a primarycomponent carrier and a plurality of secondary component carriers. In amulti-carrier aggregation mode, based on a system load (i.e.,static/dynamic load balancing), a peak data rate or a service qualityrequirement, a system may be able to allocate secondary componentcarriers to DL and/or UL asymmetrically. In using the carrieraggregation technology, the setting of the component carriers may beprovided to a user equipment by a base station after RRC connectionprocedure. In this case, the RRC connection may mean that a radioresource is allocated to a user equipment based on RRC signalingexchanged between an RRC layer of the user equipment and a network viaSRB. After completion of the RRC connection procedure between the userequipment and the base station, the user equipment may be provided bythe base station with the setting information on the primary componentcarrier and the secondary component carrier. The setting information onthe secondary component carrier may include addition/deletion (oractivation/deactivation) of the secondary component carrier. Therefore,in order to activate a secondary component carrier between a basestation and a user equipment or deactivate a previous secondarycomponent carrier, it may be necessary to perform an exchange of RRCsignaling and MAC control element.

The activation or deactivation of the secondary component carrier may bedetermined by a base station based on a quality of service (QoS), a loadcondition of carrier and other factors. And, the base station may beable to instruct a user equipment of secondary component carrier settingusing a control message including such information as an indication type(activation/deactivation) for DL/UL, a secondary component carrier listand the like.

FIG. 6 is a conceptual diagram for dual connectivity (DC) between aMaster Cell Group (MCG) and a Secondary Cell Group (SCG).

The dual connectivity means that the UE can be connected to both aMaster eNode-B (MeNB) and a Secondary eNode-B (SeNB) at the same time.The MCG is a group of serving cells associated with the MeNB, comprisingof a PCell and optionally one or more SCells. And the SCG is a group ofserving cells associated with the SeNB, comprising of the special SCelland optionally one or more SCells. The MeNB is an eNB which terminatesat least S1-MME (S1 for the control plane) and the SeNB is an eNB thatis providing additional radio resources for the UE but is not the MeNB.

With dual connectivity, some of the data radio bearers (DRBs) can beoffloaded to the SCG to provide high throughput while keeping schedulingradio bearers (SRBs) or other DRBs in the MCG to reduce the handoverpossibility. The MCG is operated by the MeNB via the frequency of f1,and the SCG is operated by the SeNB via the frequency of f2. Thefrequency f1 and f2 may be equal. The backhaul interface (BH) betweenthe MeNB and the SeNB is non-ideal (e.g. X2 interface), which means thatthere is considerable delay in the backhaul and therefore thecentralized scheduling in one node is not possible.

FIG. 7a is a conceptual diagram for C-Plane connectivity of basestations involved in dual connectivity, and FIG. 7b is a conceptualdiagram for U-Plane connectivity of base stations involved in dualconnectivity.

FIG. 7a shows C-plane (Control Plane) connectivity of eNBs involved indual connectivity for a certain UE. The MeNB is C-plane connected to theMME via S1-MME, the MeNB and the SeNB are interconnected via X2-C(X2-Control plane). As FIG. 7a , Inter-eNB control plane signaling fordual connectivity is performed by means of X2 interface signaling.Control plane signaling towards the MME is performed by means of S1interface signaling. There is only one S1-MME connection per UE betweenthe MeNB and the MME. Each eNB should be able to handle UEsindependently, i.e. provide the PCell to some UEs while providingSCell(s) for SCG to others. Each eNB involved in dual connectivity for acertain UE owns its radio resources and is primarily responsible forallocating radio resources of its cells, respective coordination betweenMeNB and SeNB is performed by means of X2 interface signaling.

FIG. 7b shows U-plane connectivity of eNBs involved in dual connectivityfor a certain UE. U-plane connectivity depends on the bearer optionconfigured: i) For MCG bearers, the MeNB is U-plane connected to theS-GW via S1-U, the SeNB is not involved in the transport of user planedata, ii) For split bearers, the MeNB is U-plane connected to the S-GWvia S1-U and in addition, the MeNB and the SeNB are interconnected viaX2-U, and iii) For SCG bearers, the SeNB is directly connected with theS-GW via S1-U. If only MCG and split bearers are configured, there is noS1-U termination in the SeNB. In the dual connectivity, enhancement ofthe small cell is required in order to data offloading from the group ofmacro cells to the group of small cells. Since the small cells can bedeployed apart from the macro cells, multiple schedulers can beseparately located in different nodes and operate independently from theUE point of view. This means that different scheduling node wouldencounter different radio resource environment, and hence, eachscheduling node may have different scheduling results.

FIG. 8 is a conceptual diagram for radio protocol architecture for dualconnectivity.

E-UTRAN of the present example can support dual connectivity operationwhereby a multiple receptions/transmissions (RX/TX) UE in RRC_CONNECTEDis configured to utilize radio resources provided by two distinctschedulers, located in two eNBs (or base stations) connected via anon-ideal backhaul over the X2 interface. The eNBs involved in dualconnectivity for a certain UE may assume two different roles: an eNB mayeither act as the MeNB or as the SeNB. In dual connectivity, a UE can beconnected to one MeNB and one SeNB.

In the dual connectivity operation, the radio protocol architecture thata particular bearer uses depends on how the bearer is setup. Threealternatives exist, MCG bearer (801), split bearer (803) and SCG bearer(805). Those three alternatives are depicted on FIG. 8. The SRBs(Signaling Radio Bearers) are always of the MCG bearer and thereforeonly use the radio resources provided by the MeNB. The MCG bearer (801)is a radio protocol only located in the MeNB to use MeNB resources onlyin the dual connectivity. And the SCG bearer (805) is a radio protocolonly located in the SeNB to use SeNB resources in the dual connectivity.

Specially, the split bearer (803) is a radio protocol located in boththe MeNB and the SeNB to use both MeNB and SeNB resources in the dualconnectivity and the split bearer (803) may be a radio bearer comprisingone Packet Data Convergence Protocol (PDCP) entity, two Radio LinkControl (RLC) entities and two Medium Access Control (MAC) entities forone direction. Specially, the dual connectivity operation can also bedescribed as having at least one bearer configured to use radioresources provided by the SeNB.

FIG. 9 is a diagram for a general overview of the LTE protocolarchitecture for the downlink.

A general overview of the LTE protocol architecture for the downlink isillustrated in FIG. 9. Furthermore, the LTE protocol structure relatedto uplink transmissions is similar to the downlink structure in FIG. 9,although there are differences with respect to transport formatselection and multi-antenna transmission.

Data to be transmitted in the downlink enters in the form of IP packetson one of the SAE bearers (901). Prior to transmission over the radiointerface, incoming IP packets are passed through multiple protocolentities, summarized below and described in more detail in the followingsections:

-   -   Packet Data Convergence Protocol (PDCP, 903) performs IP header        compression to reduce the number of bits necessary to transmit        over the radio interface. The header-compression mechanism is        based on ROHC, a standardized header-compression algorithm used        in WCDMA as well as several other mobile-communication        standards. PDCP (903) is also responsible for ciphering and        integrity protection of the transmitted data. At the receiver        side, the PDCP protocol performs the corresponding deciphering        and decompression operations. There is one PDCP entity per radio        bearer configured for a mobile terminal.    -   Radio Link Control (RLC, 905) is responsible for        segmentation/concatenation, retransmission handling, and        in-sequence delivery to higher layers. Unlike WCDMA, the RLC        protocol is located in the eNodeB since there is only a single        type of node in the LTE radio-access-network architecture. The        RLC (905) offers services to the PDCP (903) in the form of radio        bearers. There is one RLC entity per radio bearer configured for        a terminal.    -   Medium Access Control (MAC, 907) handles hybrid-ARQ        retransmissions and uplink and downlink scheduling. The        scheduling functionality is located in the eNodeB, which has one        MAC entity per cell, for both uplink and downlink. The        hybrid-ARQ protocol part is present in both the transmitting and        receiving end of the MAC protocol. The MAC (907) offers services        to the RLC (905) in the form of logical channels (909).    -   Physical Layer (PHY, 911), handles coding/decoding,        modulation/demodulation, multi-antenna mapping, and other        typical physical layer functions. The physical layer (911)        offers services to the MAC layer (907) in the form of transport        channels (913).

The MAC (907) offers services to the RLC (905) in the form of logicalchannels (909). A logical channel (909) is defined by the type ofinformation it carries and are generally classified into controlchannels, used for transmission of control and configuration informationnecessary for operating an LTE system, and traffic channels, used forthe user data.

The set of logical-channel types specified for LTE includes:

-   -   Broadcast Control Channel (BCCH), used for transmission of        system control information from the network to all mobile        terminals in a cell. Prior to accessing the system, a mobile        terminal needs to read the information transmitted on the BCCH        to find out how the system is configured, for example the        bandwidth of the system.    -   Paging Control Channel (PCCH), used for paging of mobile        terminals whose location on cell level is not known to the        network and the paging message therefore needs to be transmitted        in multiple cells.    -   Dedicated Control Channel (DCCH), used for transmission of        control information to/from a mobile terminal. This channel is        used for individual configuration of mobile terminals such as        different handover messages.    -   Multicast Control Channel (MCCH), used for transmission of        control information required for reception of the MTCH.    -   Dedicated Traffic Channel (DTCH), used for transmission of user        data to/from a mobile terminal. This is the logical channel type        used for transmission of all uplink and non-MBMS downlink user        data.    -   Multicast Traffic Channel (MTCH), used for downlink transmission        of MBMS services.

FIG. 10 is a diagram for prioritization of two logical channels forthree different uplink grants.

Multiple logical channels of different priorities can be multiplexedinto the same transport block using the same MAC multiplexingfunctionality as in the downlink. However, unlike the downlink case,where the prioritization is under control of the scheduler and up to theimplementation, the uplink multiplexing is done according to a set ofwell-defined rules in the terminal as a scheduling grant applies to aspecific uplink carrier of a terminal, not to a specific radio bearerwithin the terminal. Using radio-bearer-specific scheduling grants wouldincrease the control signaling overhead in the downlink and henceper-terminal scheduling is used in LTE.

The simplest multiplexing rule would be to serve logical channels instrict priority order. However, this may result in starvation oflower-priority channels; all resources would be given to thehigh-priority channel until its transmission buffer is empty. Typically,an operator would instead like to provide at least some throughput forlow-priority services as well. Therefore, for each logical channel in anLTE terminal, a prioritized data rate is configured in addition to thepriority value. The logical channels are then served in decreasingpriority order up to their prioritized data rate, which avoidsstarvation as long as the scheduled data rate is at least as large asthe sum of the prioritized data rates. Beyond the prioritized datarates, channels are served in strict priority order until the grant isfully exploited or the buffer is empty. This is illustrated in FIG. 10.

Regarding FIG. 10, it may be assumed that a priority of the logicalchannel 1 (LCH 1) is higher than a priority of the logical channel 2(LCH 2). In case of (A), all prioritized data of the LCH 1 can betransmitted and a portion of prioritized data of the LCH 2 can betransmitted until amount of the scheduled data rate. In case of (B), allprioritized data of the LCH 1 and all prioritized data of the LCH 2 canbe transmitted. In case of (C) all prioritized data of the LCH 1 and allprioritized data of the LCH 2 can be transmitted and a portion of dataof the LCH 1 can be further transmitted.

FIG. 11 is a diagram for signaling of buffer status and power-headroomreports.

The scheduler needs knowledge about the amount of data awaitingtransmission from the terminals to assign the proper amount of uplinkresources. Obviously, there is no need to provide uplink resources to aterminal with no data to transmit as this would only result in theterminal performing padding to fill up the granted resources. Hence, asa minimum, the scheduler needs to know whether the terminal has data totransmit and should be given a grant. This is known as a schedulingrequest.

The use of a single bit for the scheduling request is motivated by thedesire to keep the uplink overhead small, as a multi-bit schedulingrequest would come at a higher cost. A consequence of the single bitscheduling request is the limited knowledge at the eNodeB about thebuffer situation at the terminal when receiving such a request.Different scheduler implementations handle this differently. Onepossibility is to assign a small amount of resources to ensure that theterminal can exploit them efficiently without becoming power limited.Once the terminal has started to transmit on the UL-SCH, more detailedinformation about the buffer status and power headroom can be providedthrough the inband MAC control message, as discussed below.

Terminals that already have a valid grant obviously do not need torequest uplink resources. However, to allow the scheduler to determinethe amount of resources to grant to each terminal in future subframes,information about the buffer situation and the power availability isuseful, as discussed above. This information is provided to thescheduler as part of the uplink transmission through MAC controlelement. The LCID field in one of the MAC subheaders is set to areserved value indicating the presence of a buffer status report, asillustrated in FIG. 11.

From a scheduling perspective, buffer information for each logicalchannel is beneficial, although this could result in a significantoverhead. Logical channels are therefore grouped into logical-channelgroups and the reporting is done per group. The buffer-size field in abuffer-status report indicates the amount of data awaiting transmissionacross all logical channels in a logical-channel group. A buffer statusreport represents one or all four logical-channel groups and can betriggered for the following reasons:

i) Arrival of data with higher priority than currently in thetransmission buffer—that is, data in a logical-channel group with higherpriority than the one currently being transmitted—as this may impact thescheduling decision.

ii) Change of serving cell, in which case a buffer-status report isuseful to provide the new serving cell with information about thesituation in the terminal.

iii) Periodically as controlled by a timer.

iv) Instead of padding. If the amount of padding required to match thescheduled transport block size is larger than a buffer-status report, abuffer-status report is inserted. Clearly it is better to exploit theavailable payload for useful scheduling information instead of paddingif possible.

Data Available for Transmission in a PDCP Entity

For the purpose of MAC buffer status reporting, the UE shall considerPDCP Control PDUs, as well as the following as data available fortransmission in the PDCP entity:

For SDUs for which no PDU has been submitted to lower layers: i) the SDUitself, if the SDU has not yet been processed by PDCP, or ii) the PDU ifthe SDU has been processed by PDCP.

In addition, for radio bearers that are mapped on RLC AM, if the PDCPentity has previously performed the re-establishment procedure, the UEshall also consider the following as data available for transmission inthe PDCP entity:

For SDUs for which a corresponding PDU has only been submitted to lowerlayers prior to the PDCP re-establishment, starting from the first SDUfor which the delivery of the corresponding PDUs has not been confirmedby the lower layer, except the SDUs which are indicated as successfullydelivered by the PDCP status report, if received: i) the SDU, if it hasnot yet been processed by PDCP, or ii) the PDU once it has beenprocessed by PDCP.

Data Available for Transmission in a RLC Entity

For the purpose of MAC buffer status reporting, the UE shall considerthe following as data available for transmission in the entity: i) RLCSDUs, or segments thereof, that have not yet been included in an RLCdata PDU, ii) RLC data PDUs, or portions thereof, that are pending forretransmission (RLC AM).

In addition, if a STATUS PDU has been triggered and t-StatusProhibit isnot running or has expired, the UE shall estimate the size of the STATUSPDU that will be transmitted in the next transmission opportunity, andconsider this as data available for transmission in the RLC layer.

Buffer Status Reporting (BSR)

The Buffer Status Reporting (BSR) procedure is used to provide a servingeNB with information about the amount of data available for transmission(DAT) in the UL buffers of the UE. RRC may control BSR reporting byconfiguring the two timers periodicBSR-Timer and retxBSR-Timer and by,for each logical channel, optionally signalling Logical Channel Groupwhich allocates the logical channel to an LCG (Logical Channel Group).

For the Buffer Status reporting procedure, the UE may consider all radiobearers which are not suspended and may consider radio bearers which aresuspended. A Buffer Status Report (BSR) may be triggered if any of thefollowing events occur:

-   -   UL data, for a logical channel which belongs to a LCG, becomes        available for transmission in the RLC entity or in the PDCP        entity and either the data belongs to a logical channel with        higher priority than the priorities of the logical channels        which belong to any LCG and for which data is already available        for transmission, or there is no data available for transmission        for any of the logical channels which belong to a LCG, in which        case the BSR is referred below to as “Regular BSR”;    -   UL resources are allocated and number of padding bits is equal        to or larger than the size of the Buffer Status Report MAC        control element plus its subheader, in which case the BSR is        referred below to as “Padding BSR”;    -   retxBSR-Timer expires and the UE has data available for        transmission for any of the logical channels which belong to a        LCG, in which case the BSR is referred below to as “Regular        BSR”;    -   periodicBSR-Timer expires, in which case the BSR is referred        below to as “Periodic BSR”.

A MAC PDU may contain at most one MAC BSR control element, even whenmultiple events trigger a BSR by the time a BSR can be transmitted inwhich case the Regular BSR and the Periodic BSR shall have precedenceover the padding BSR.

The UE may restart retxBSR-Timer upon indication of a grant fortransmission of new data on any UL-SCH.

All triggered BSRs may be cancelled in case UL grants in this subframecan accommodate all pending data available for transmission but is notsufficient to additionally accommodate the BSR MAC control element plusits subheader. All triggered BSRs shall be cancelled when a BSR isincluded in a MAC PDU for transmission.

The UE shall transmit at most one Regular/Periodic BSR in a TTI. If theUE is requested to transmit multiple MAC PDUs in a TTI, it may include apadding BSR in any of the MAC PDUs which do not contain aRegular/Periodic BSR.

All BSRs transmitted in a TTI always reflect the buffer status after allMAC PDUs have been built for this TTI. Each LCG shall report at the mostone buffer status value per TTI and this value shall be reported in allBSRs reporting buffer status for this LCG.

FIG. 12 is a conceptual diagram for one of radio protocol architecturefor dual connectivity.

‘Data available for transmission’ is defined in PDCP and RLC layers tobe used for Buffer Status Reporting (BSR), Logical ChannelPrioritization (LCP), and Random Access Preamble Group (RAPG) selectionin MAC layer. In the prior art, there are only one PDCP entity and oneRLC entity for one direction (i.e. uplink or downlink) in a RadioBearer, and thus, when the UE calculates ‘data available fortransmission’, it just sums up the data available for transmission inPDCP and that in RLC.

However, in LTE Rel-12, a new study on dual connectivity, i.e. UE isconnected to both MeNB (1201) and SeNB (1203), as shown in FIG. 12. Inthis figure, the interface between MeNB (1201) and SeNB (1203) is calledXn interface (1205). The Xn interface (1205) is assumed to be non-ideal;i.e. the delay in Xn interface could be up to 60 ms, but it is notlimited thereto.

To support dual connectivity, one of the potential solutions is for theUE (1207) to transmit data to both MeNB (1201) and SeNB (1203) utilizinga new RB structure called dual RLC/MAC scheme, where a single RB has onePDCP—two RLC—two MAC for one direction, and RLC/MAC pair is configuredfor each cell, as shown in FIG. 12. In this figure, BE-DRB (1209) standsfor DRB for Best Effort traffic.

In this case, the MAC functions addressed above, i.e. buffer statusreporting, are performed in each MAC, since the UL resource schedulingnode is located in different node in the network side, i.e. one in MeNB(1201) and the other in SeNB (1203).

The problem is how to use the information ‘data available fortransmission in PDCP’ in the MAC functions. If each MAC utilizes thesame information of ‘data available for transmission in PDCP’, both theMeNB and the SeNB would allocate UL resource that can cope with ‘dataavailable for transmission in PDCP’, in which case the ‘data availablefor transmission in PDCP’ is considered twice, and it leads to wastageof radio resource.

FIG. 13 is a conceptual diagram for reporting amount of data availablefor transmission according to embodiments of the present invention.

To prevent a first base station and a second base station toover-allocate the UL resource to the UE having dual RLC/MAC scheme, itis invented that the UE divides ‘Data Available for Transmission inPDCP’ (hereafter called DATP) to each MAC based on ratio.

The ratio may indicate ratio of “amount of PDCP data transmitted toRLC1” to “amount of PDCP data transmitted to RLC2” where RLC1 and RLC2are connected to the PDCP entity, but it is not limited thereto. TheRLC1 is for the first base station and RLC2 is for the second basestation. Desirably, the first base station may be a MeNB and the secondbase station may be a SeNB, and vice versa.

The ratio may be configured by the first base station or the second basestation through RRC signaling or PDCP signaling or MAC signaling, when aradio bearer is configured or reconfigured (S1301). The ration is forcalculating amount of Data Available for Transmission (DAT) in a PDCP(Packet Data Convergence Protocol) entity. The ratio can be a form ofratio “DATP-1 (DATP for MAC in the first base station):DATP-2 (DATP forMAC in the second base station”, or percentile amount of DATP-2 comparedto DATP-1, or vice versa, or any type of information that indicates theamount of data that can be used to divide the DATP to DATP-1 and DATP-2.

The UE can calculate an amount of DAT when data is arrived in the PDCPentity (S1303).

When the UE calculates the DATP and divides it into DATP-1 and DATP-2,if the DATP is less than a threshold, the UE does not divide the DATPinto DATP-1 and DATP-2. The threshold may be called as “minimum amountof data in PDCP”.

When the result of the step of S1303 is “X”, consequently, the UE canset a first amount of DAT (DATP-1) as the calculated amount of DAT (X)and a second amount of DAT (DATP-2) as 0 or the first amount of DAT(DATP-1) as 0 and the second amount of DAT (DATP-2) as the calculatedamount of DAT (X)” when DATP is less than the threshold (S1305). Thismethod aims at reducing the waste of UL resource considering the minimumamount of UL resources to be assigned to the UE.

The UE may receive the information related to the threshold from thefirst base station or the second base station. The information relatedto the threshold may indicate the minimum amount of data in PDCP inbyte.

The UE may receive configuration information through RRC signaling fromthe first base station for the second base station. When the UEcalculates DATP (S1303), if it is less than the threshold, the UE canselect one of DATP-1 or DATP-2 by following the priority received fromthe first base station/the second base station or can randomly selectone of DATP-1 or DATP-2.

The priority indicates which base station is prioritized over other basestation. Then, the UE sets the selected DATP-1 or DATP-2 equal to DATP.For example, when the DATP is less than the threshold, if the DATP-1 isprioritized over the DATP-2 by the first base station or the second basestation, the UE divides DATP into DATP-1 and DATP-2 so that “DATP-M=Xbytes” and “DATP-S=0 byte”.

After the step of S1305, the UE can report the amount of DAT to the BS(S1307). In this case, the UE can report the amount of DATP-1 to thefirst base station and can report the amount of DATP-2 to the secondbase station. If the amount of DATP-2 is ‘0’, the UE can report theamount of DATP-1 to the first base station but the UE may not report theamount of DATP-2 to the second base station.

Meanwhile, when the UE calculates the DATP and divides it into DATP-1and DATP-2, if the DATP is equal to or more than the threshold, the UEmay divide the DATP into DATP-1 and DATP-2 based on the ratio (S1309).In this case, the UE may set a first amount of DAT (DATP-1) as ‘Y’ and asecond amount of DAT (DATP-2) as ‘Z’ based on the ratio when DATP isequal to or more than the threshold (S1311).

When the UE calculates the DATP and divides it into DATP-1 and DATP-2using the ratio, there is a case that the DATP-1 and DATP-2 are not themultiple of bytes. Since the UL resource is always assigned by bytes,the UE aligns DATP-1 and DATP-2 with the multiple of bytes as follows:

If the DATP-1 and DATP-2 are not the multiple of bytes,

The UE rounds off DATP-1 and DATP-2 to the nearest integer. For example,when the DATP=101 bytes, if the UE divides the DATP using the ratio of3:7, the DATP-1=30.3 bytes and DATP-2=70.7 bytes. In this case, the UErounds off DATP-1 and DATP-2 so that the DATP-1 is 30 bytes and DATP-2is 71 bytes. The UE also can round off/roundup/rounddown one or both ofDATP-1 and DATP-2.

The UE adds the remaining amount of data to DATP-1 or DATP-2. Forexample, if the DATP=101 bytes, the DATP-M=30.3 bytes and DATP-S=70.7bytes. In this case, the UE adds the remaining 0.3 bytes of DATP-1 tothe DATP-2 so that the DATP-1 is 30 bytes and DATP-2 is 71 bytes.

After the step of S1311, the UE can report the amount of DAT to the BS(S1313). In this case, the UE can report the amount of DATP-1 to thefirst base station and can report the amount of DATP-2 to the secondbase station.

FIG. 14 is a conceptual diagram for triggering a buffer status reportingaccording to embodiments of the present invention.

The Buffer Status Reporting (BSR) procedure is used to provide a servingBS with information about the amount of data available for transmission(DAT) in the UL buffers of the UE. For the Buffer Status reportingprocedure, the UE may consider all radio bearers which are not suspendedand may consider radio bearers which are suspended.

In this prior art, a Buffer Status Report (BSR) may be triggered when ULdata, for a logical channel which belongs to a LCG, becomes availablefor transmission in the RLC entity or in the PDCP entity and either thedata belongs to a logical channel with higher priority than thepriorities of the logical channels which belong to any LCG and for whichdata is already available for transmission, or there is no dataavailable for transmission for any of the logical channels which belongto a LCG, in which case the BSR is referred below to as “Regular BSR”.That means, when data belongs to a logical channel with same priority asthe priorities of the logical channels which belong to any LCG and forwhich data is already available for transmission, the BSR is nottriggered.

However, in dual connectivity system, the UE is required to trigger theBSR although data belongs to a logical channel with same priority as thepriorities of the logical channels which belong to any LCG and for whichdata is already available for transmission.

Regarding FIG. 14, when the first data is arrived in a protocol entity,the UE can calculate an amount of first DAT (S1401). Desirably, theprotocol entity is a PDCP entity, but it is not limited thereto.

When the result of the step of S1401 is “X”, if the X is less than athreshold, the UE can set an amount of DAT for a first logical channel(DATP-1) as the calculated amount of DAT (X) and an amount of DAT for asecond logical channel (DATP-2) as ‘zero’. The first logical channel isfor the first BS and the second logical channel is for the second BS. Onthe other hand, if the X is equal to or more than a threshold, the UEmay trigger a BSR (S1403).

After the step of S1401, when the second data is arrived in a protocolentity, the UE can calculate an amount of second DAT (S1405). When theresult of the step of S1405 is “Y”, if the Y is equal to or more thanthe threshold, the UE can trigger the BSR (S1407) although data belongsto a logical channel with same priority as the priorities of the logicalchannels which belong to any LCG and for which data is already availablefor transmission. If the Y is less than the threshold, the UE cannottrigger the BSR (S1409).

In conclusion, in view of the second logical channel, the second logicalchannel has a lower priority than the first logical channel. Thus, inthe step of the S1401, if X is less than the threshold, an amount of DATfor a second logical channel is set to ‘0’. BSR of the second logicalchannel is not triggered despite having the data. In the step of S1405,if Y is equal to or more than the threshold, the amount of DAT for asecond logical channel is set to some byte based on the certain ratio.In this case, the BSR of the second logical channel is required totrigger the BSR although the data belongs to a logical channel with samepriority as the priorities of the logical channels which belong to anyLCG and for which data is already available for transmission. Thus, theUE can trigger the BSR when the amount of first DAT is less than athreshold and the amount of second DAT is more than the threshold.

FIG. 15 is conceptual diagram an exemplary according to embodiments ofthe present invention.

An example procedure of this invention is shown in FIG. 15, but this isone of example according to embodiments of the present invention, so itis not limited thereto.

The UE receives ratio information of a RB identified by RB ID from anMeNB or a SeNB. In this example, the ratio is set to 3:7. The UE alsoreceives threshold information. The threshold is set to 20 bytes andDATP-M is prioritized over DATP-S in this example (S1501). The ‘DATP-M’is Data Available for Transmission in PDCP for the MeNB and the ‘DATP-S’is Data Available for Transmission in PDCP for the SeNB.

The first data for the indicated RB are arrived (S1503). The UEcalculates the DATP. Since the DATP is 10 bytes and less than 20 bytes,the UE does not divide it into DATP-M and DATP-S so that DATP-M=10 bytesand DATP-S=0 byte (S1505).

For the indicated RB, the UE calculates the DATR-M (Data Available forTransmission in RLC for the MeNB) and DATR-S (Data Available forTransmission in RLC for the SeNB). In this example, DATR-M=0 bytes andDATR-S=0 bytes (S1507). For the indicated RB, the UE calculates DAT-M(Data Available for Transmission for the MeNB) and DAT-S (Data Availablefor Transmission for the SeNB) such as DAT-M=DATP-M+DATR-M andDAT-S=DATP-S+DATR-S. In this example, DAT-M=0+10=10 bytes, andDAT-S=0+0=0 bytes (S1509). Since this is an initial transmission and theDATP is less than threshold, the UE sends the BSR only to the MeNB(S1511).

For the indicated RB, the data belonging to the same logical channel arearrived (S1513). For the indicated RB, the UE calculates the DATP. Sincethe DATP is 30 bytes, which is more than 20 bytes, and the previous DATPis less than the threshold, the UE triggers BSR and divides it intoDATP-M and DATP-S using ratio (S1515). Consequently, DATP-M=9 bytes andDATP-S=21 byte.

For the indicated RB, the UE calculates the DATR-M and DATR-S. In thisexample, DATR-M=2 bytes and DATR-S=0 bytes (S1517).

For the indicated RB, the UE calculates DAT-M and DAT-S. In thisexample, DAT-M=2+9=11 bytes, and DAT-S=0+21=21 bytes (S1519). The UEsends the BSR to both of MeNB and SeNB with the calculated buffer size(S1521) because the BSR is triggered in the step of S1515.

FIG. 16 is a block diagram of a communication apparatus according to anembodiment of the present invention.

The apparatus shown in FIG. 16 can be a user equipment (UE) and/or eNBadapted to perform the above mechanism, but it can be any apparatus forperforming the same operation.

As shown in FIG. 16, the apparatus may comprises a DSP/microprocessor(110) and RF module (transmiceiver; 135). The DSP/microprocessor (110)is electrically connected with the transceiver (135) and controls it.The apparatus may further include power management module (105), battery(155), display (115), keypad (120), SIM card (125), memory device (130),speaker (145) and input device (150), based on its implementation anddesigner's choice.

Specifically, FIG. 16 may represent a UE comprising a receiver (135)configured to receive a request message from a network, and atransmitter (135) configured to transmit the transmission or receptiontiming information to the network. These receiver and the transmittercan constitute the transceiver (135). The UE further comprises aprocessor (110) connected to the transceiver (135: receiver andtransmitter).

Also, FIG. 17 may represent a network apparatus comprising a transmitter(135) configured to transmit a request message to a UE and a receiver(135) configured to receive the transmission or reception timinginformation from the UE. These transmitter and receiver may constitutethe transceiver (135). The network further comprises a processor (110)connected to the transmitter and the receiver. This processor (110) maybe configured to calculate latency based on the transmission orreception timing information.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

The embodiments of the present invention described herein below arecombinations of elements and features of the present invention. Theelements or features may be considered selective unless otherwisementioned. Each element or feature may be practiced without beingcombined with other elements or features. Further, an embodiment of thepresent invention may be constructed by combining parts of the elementsand/or features. Operation orders described in embodiments of thepresent invention may be rearranged. Some constructions of any oneembodiment may be included in another embodiment and may be replacedwith corresponding constructions of another embodiment. It is obvious tothose skilled in the art that claims that are not explicitly cited ineach other in the appended claims may be presented in combination as anembodiment of the present invention or included as a new claim bysubsequent amendment after the application is filed.

In the embodiments of the present invention, a specific operationdescribed as performed by the BS may be performed by an upper node ofthe BS. Namely, it is apparent that, in a network comprised of aplurality of network nodes including a BS, various operations performedfor communication with an MS may be performed by the BS, or networknodes other than the BS. The term eNB′ may be replaced with the term‘fixed station’, ‘Node B’, ‘Base Station (BS)’, ‘access point’, etc.

The above-described embodiments may be implemented by various means, forexample, by hardware, firmware, software, or a combination thereof.

In a hardware configuration, the method according to the embodiments ofthe present invention may be implemented by one or more ApplicationSpecific Integrated Circuits (ASICs), Digital Signal Processors (DSPs),Digital Signal Processing Devices (DSPDs), Programmable Logic Devices(PLDs), Field Programmable Gate Arrays (FPGAs), processors, controllers,microcontrollers, or microprocessors.

In a firmware or software configuration, the method according to theembodiments of the present invention may be implemented in the form ofmodules, procedures, functions, etc. performing the above-describedfunctions or operations. Software code may be stored in a memory unitand executed by a processor. The memory unit may be located at theinterior or exterior of the processor and may transmit and receive datato and from the processor via various known means.

Those skilled in the art will appreciate that the present invention maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent invention. The above embodiments are therefore to be construedin all aspects as illustrative and not restrictive. The scope of theinvention should be determined by the appended claims and their legalequivalents, not by the above description, and all changes coming withinthe meaning and equivalency range of the appended claims are intended tobe embraced therein.

INDUSTRIAL APPLICABILITY

While the above-described method has been described centering on anexample applied to the 3GPP LTE system, the present invention isapplicable to a variety of wireless communication systems in addition tothe 3GPP LTE system.

1. A method for a user equipment (UE) operating in a wirelesscommunication system comprising a first base station (BS) and a secondBS, the method comprising: calculating an amount of first DAT when thefirst data is arrived in a protocol entity, wherein the amount of firstDAT is less than a threshold; calculating an amount of second DAT whenthe second data is arrived in the protocol entity, wherein the seconddata is arrived after the first data is arrived in the protocol entity;and triggering a buffer status report if the amount of second DAT ismore than the threshold.
 2. The method according to claim 1, the methodfurther comprising: setting an amount of DAT for a first logical channelas the calculated amount of first DAT and an amount of DAT for a secondlogical channel as ‘zero’, if the amount of first DAT is less than thethreshold, wherein the first logical channel is for the first BS and thesecond logical channel is for the second BS.
 3. The method according toclaim 2, the method further comprising: dividing the calculated amountof second DAT into the amount of DAT for the first logical channel andthe amount of DAT for the second logical channel based on ratio if theamount of second DAT is equal to or more than the threshold.
 4. Themethod according to claim 1, wherein the buffer status report istransmitted to the second BS.
 5. The method according to claim 1, themethod further comprising: receiving the threshold from at least thefirst BS or the second BS.
 6. The method according to claim 1, whereinthe protocol entity is a Packet Data Convergence Protocol (PDCP) entity.7. The method according to claim 6, wherein PDCP entity has two RadioLink Control (RLC) entities and two Medium Access Control (MAC) entitiesfor one logical channel.
 8. A user equipment (UE) operating in awireless communication system comprising a first base station (BS) and asecond BS, the UE comprising: an RF (radio frequency) module; and aprocessor configured to control the RF module, wherein the processor isconfigured to calculate an amount of first DAT when the first data isarrived in a protocol entity, wherein the amount of first DAT is lessthan a threshold, to calculate an amount of second DAT when the seconddata is arrived in the protocol entity, wherein the second data isarrived after the first data is arrived in the protocol entity, and totrigger a buffer status report if the amount of second DAT is more thanthe threshold.
 9. The UE according to claim 8, wherein the processor isfurther configured to set an amount of DAT for a first logical channelas the calculated amount of first DAT and an amount of DAT for a secondlogical channel as ‘zero’, if the amount of first DAT is less than thethreshold, wherein the first logical channel is for the first BS and thesecond logical channel is for the second BS.
 10. The UE according toclaim 9, wherein the processor is further configured to divide thecalculated amount of second DAT into an amount of DAT for the firstlogical channel and an amount of DAT for the second logical channelbased on ratio if the amount of second DAT is equal to or more than thethreshold.
 11. The UE according to claim 8, wherein the buffer statusreport buffer status report is transmitted to the second BS.
 12. The UEaccording to claim 8, wherein the processor is further configured toreceive the threshold from at least the first BS or the second BS. 13.The UE according to claim 8, wherein the protocol entity is a PacketData Convergence Protocol (PDCP) entity.
 14. The UE according to claim13, wherein PDCP entity has two Radio Link Control (RLC) entities andtwo Medium Access Control (MAC) entities for one logical channel.